Pairs of complementary two-tone complex periodic signals produce distinct pitch differences if the constituent tones differ in amplitude. Our preliminary work indicates that the discriminability of such signal pairs may be based upon differences in a weighted average of the instantaneous frequency functions of the signals. The proposed research should further our understanding of the peripheral frequency analysis performed by the human ear. We plan to build upon our preliminary results using both frequency discrimination tasks and pitch-matching procedures with the same signal set and the same listeners. This phase of the work will establish the bandwidth of the peripheral auditory system for the frequency resolution of complex tones. The role of the instantaneous frequency function in pitch perception will be investigated. A final phase of the study will use a complex tone synthesized from three two-tone complexes to investigate the influence of stimulus fine-structure upon periodicity pitch perception.